civic fight led by a former u.s. first lady helped save grand central. >> if you destroy your past, something in people die. >> reporter: now in a new york minute you can spot a wedding, a modeling shoot -- >> it's absolutely stunning. >> reporter: and a squash tournament. >> with these mysteries and things -- >> reporter: tour guide dan bruker revealed the secrets of grand central. look up, people don't even notice a ceiling to mirror the constellation. >> move, move, chop, chop, in the corn,er, let's go! >> reporter: another secret is the whispering gallery. >> even though i am standing 30 feet away from you, speaking in a low voice, you can probably hear every word i'm saying. we are now descending into the deepest basement in new york city. >> reporter: this sub basement is not even on grand central maps. and it hums with history. >> this is the most top secret location inside grand central terminal, the m-42. more than decades ago, troops stood guard to guard against tax on the power system. >> there was a great